Project Abstract (Topic code HLS18-02) Signi?cant progress has been achieved in developing precision therapies for cystic ?brosis (CF); however, highly effective treatments that target the cystic ?brosis transmembrane conductance regulator (CFTR) are not yet available for every patient with CF. Therapeutic efforts have recently focused on correcting the defect resulting from the common F508del variant, as well as many less frequent missense alleles. Of the missense variants, more than 500 have been noted in 10 individuals or fewer worldwide. The rarity of these patients precludes standard randomized controlled trials to test ef?cacy of new CFTR therapeutics in the clinical pipelines. Thus reliable in vitro cell-based models capable of predicting drug ef?cacy using patient-derived cells to support individualized treatment plans and translational research are essential. Primary human nasal or bronchial epithelial cells have emerged as strong predictive tools to study rare CFTR variants in a near-native context. Despite their outstanding value, primary nasal or bronchial epithelial cells are difficult to grow and expand using conventional cell culture media, impeding their employment in evaluating CFTR-targeted precision therapy. Here we propose using our patented EpiX? cell culture technology to expand airway epithelial cells from nasal brushing samples of CF patients for in vitro human cell-based models to predict individual responses to CFTR-directed therapeutics. EpiX? medium allows over trillion-fold of in vitro expansion like the conditional reprogramming method, without using feeder cells. The expanded cells can be seamlessly integrated into existing downstream differentiation protocols and put into physiological CFTR and mucociliary functional evaluations. EpiX?-expanded bronchial epithelial cells maintain CFTR and epithelial sodium channel (ENaC) functions even after trillion-fold expansion. EpiX? also supports quick and efficient expansion of a small number of basal epithelial cells, such as those derived from nasal brushing samples, to generate hundreds of millions of cells. The EpiX? medium provides a reliable, robust and easy- to-use solution that offers significant advantages over current technologies that related to the ultimate goals to identify personalized therapy for CF patients.